Induction-conduction charging of electrostatic generators



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J. G. TRUMP ET AL INDUCTION-CONDUCTION CHARGING OF ELECTROSTATICGENERATORS Filed Dec.

Dec. 21, 1954 United States Patent INDUCTIQN-CONDUCTION CHARGING OFELECTROSTATIC GENERATORS John G. Trump, Winchester, and Robert W. Cloud,Lexington, Mass., assignors to Research Corporation, New York, N. Y., acorporation of New York Application December 12, 1951, Serial No.261,244

17 Claims. (Cl. 310-5) This invention relates to high potentialelectrostatic apparatus embodying the general principles disclosed inthe U. S. patent to Robert J. Van de Graaff, No. 1,991,236, in the U. S.patent to John G. Trump, No. 2,252,668, and in the U. S. patent to JohnG. Trump and Robert W. Cloud, No. 2,503,224, and also relates to a newmethod and system pertaining thereto, and particularly to the transferof electric charge to and froma charge conveyor, and more particularlyit relates to the transfer of electric charges to and from an endlesscharge-carrying conveyor, and especially to the transfer of electriccharges to and from an endless belt or belts as used in the Van deGraaff type of electrostatic generators and accelerators.

In order that the principle of the invention may be readily understood,we will first sufliciently describe the present corona method of chargetransference, and state the limitations thereof which led to the presentinvention, and we will set forth the relative advantages of the latter,and we will then disclose, as examples, several embodiments of apparatusby each of which the method of our present invention may be practiced,and constituting a type of the system of our invention.

Present corona method of charge transference Van de Graalf electrostatichigh voltage sources consist of a well-insulated high voltage terminaland an insulating belt which transfers electric charge between thisterminal and ground. Electric charge is deposited upon this insulatingbelt or removed from it by causing ionization of the gaseous medium atthe region where this deposition or removal is to take place. This iscommonly done by presenting toward the belt an array of points or theedge of a screen or a thin metal sheet. For example, negative electriccharge is deposited upon the insulating belt by maintaining a potentialdifference between the pulley over which the belt passes and a row ofsharp points which are directed toward the pulley from the other sideofthe belt. A negative potential applied to the points results in a highelectric field which causes the ionization of the gas by the Townsendalpha process and results in the deposition of negative electric chargeupon the intervening insulating surface of the belt.

This corona method of transferring electric charge to a movinginsulating belt surface has become the conventional method for modernVan de Graaff accelerators. First applied to electrostatic highvoltagesources which operate in air at atmospheric pressure, the coronamethod is now also the universal method of charge transfer in modernelectrostatic generators insulated in compressed gases. It has been usedin apparatus insulated by gas at pressures of 400 lbs. per square inchand higher.

There are certain disadvantages in the said present corona method ofcharge transference, which we will briefly state as follows:

1. The creation of ionization for the deposition or removal of electriccharge from an insulating belt becomes increasingly difiicult withincreased gas pressure.

2. Higher voltages are required to produce the necessary ionization ofthe gaseous medium the better the dielectric strength of the gas.

3. A peculiar phenomena known as the positive pointto-plane effectintroduces special difliculties in spraying positive charge upon aninsulating surface when the gas pressure is above a certain criticalvalue.

4. Ionization results in the dissociation of gas molecules and increasestheir chemical activity with resultant tendtric field which induces theflow 2,697,793 Patented Dec. 21, 1954 ency to cause deterioration of theinsulating belt material and of the gas itself, as well as corrosion ofmetal surfaces.

5. The corona charge-transferring mechanism is extremely sensitive tothe nature of the gas, to the gas pressure, to the geometricrelationship of the points and the belt, to the sharpness of the pointsand edges, and to other factors ditiicult to control.

6. Fundamentally the corona mechanism as a means of transferring anelectric charge is undesirable because it imposes upon the gaseousinsulating medium surrounding the high voltage source the conflictingrequirements that it be capable both of readily conducting electricityat the charge-transfer regions and of insulating high voltages andgradients without ionization in other regions.

The present invention The present invention, involving method, systemand apparatus, eliminates the necessity of gaseous ionization, intransferring electric charge to and from the belt of Van de Graatfelectrostatic generators and accelerators, and while we will hereinillustrate and describe a charge conveyor of the endless belt type, itis to be understood that our charge conveyor may be any suitable movingstructure, preferably of the endless type, such as a traveling belt or alarge, rapidly rotating disk.

In accordance with our invention, and referring to the herein disclosedseveral different embodiments of beltconveyor apparatus for practicingthe same, we, in one way or manner of carrying out our novel method, usea novel, semi-conducting endless belt and electrostatically inducecharge to flow onto such belt from a metal charging member with which itis momentarily in contact, such as the lower pulley by which the belt isdriven. The elec-' of electric charge onto such belt extends beyond thepulley to a region where the belt has lost conductive contact with thesaid metal charging member, namely, the lower pulley. The resistivity ofthe belt is, as hereinafter fully disclosed, such that once suchconductive contact has been lost, the charge remains bound upon the beltwithout essential loss until it is removed at some subsequent state inthe generator process, as will be fully described.

In the accompanying figures of the drawings we have, as examples,disclosed several different embodiments of belt conveyor means for thepractice of our invention.

Fig. 1 represents in vertical transverse section, the lower part only ofan electrostatic generator of the general type disclosed in the saidpatent to Trump, No. 2,252,668, and in the said patent to Trump andCloud, No. 2,503,224, but having our invention incorporated therein anddisclosing how a negative electric charge is induced to flow on theascending run of the belt, by maintaining a positive poterfiial on theinducing plate, with respect to the ground P y;

Fig. 2 is a similar view of the upper part only, of such electrostaticgenerator, and it discloses how the electric charge is removed from theascending run of the belt by means of a conductive contact, as bycontact with the upper pulley of the generator, or by contact with asmall pulley within the electrode terminal;

Fig. 3 is a diagrammatic View of a small lengthwise extending portion ofthe belt from edge to edge thereof, wherein the semi-conducting materialis applied to the inner surface of the belt as a coating or layer, onisolated areas having the form of spaced lines extending transversely ofsaid belt;

Fig. 4 is a similar diagrammatic view, but representing the isolatedareas as a great multiplicity of dots; and

Fig. 5 is a similar diagrammatic view, but representing the isolatedareas as having the form of spaced circular generator has the main highhemispherical shape and free from external projections. In practice thesaidrelectrode 1, also referred to as the terminal, is supported in anysuitable manner, as, for example, in the manner shown in Fig. 1 of thesaid U. S. patent to Trump, No. 2,252,668. The bases of the supportingpillars or columns rest on a base plate of conductive material supportedby brackets or otherwise attached to the inner walls of a surroundingtank 1a, which is or may be such as is shown at 21 in said patent toTrump, andwhich is filled with gas, which in the practice of ourinvention may be assumed to be air, or preferably a mixture of nitrogenand carbon dioxide, maintained under a suitable pressure as, forexample, between 200 and 400 or more pounds per square inch aboveatmospheric.

The charge carrier, to the novel nature of which our invention is mainlydirected, is here, for example only, shown as in the form of an endlessbelt indicated generally at 2, and of a construction herein subsequentlyde scribed, and whereon the charges are carried upon its surface. At itslower end the belt passes about a metallic driving pulley 3, whichtherefore has a conductive surface. Such driving pulley 3 is journalledin suitable brackets on the base plate, so that the said pulley 3 has agrounded connection. In practice this lower pulley is insulated andconnected to ground through a microammeter I, this being a convenientway of measuring the current transferred to the belt from the lowerpulley. The said pulley is driven, preferably, by an electric motor towhich current is supplied by conductors entering the walls of the tankthrough a suitable bushing.

The said belt 2 runs vertically upward and then downward in a parallelrun or series of runs, depending upon the number of the belts used,passing into and out of the hollow electrode or terminal 1, and over ametallic pulley or pulleys 4, within said electrode 1, and whichtherefore has a conductive surface similar to that of the metallicdriving pulley 3. The said pulley 4 is journalled in but is insulatedfrom brackets supported by the ring referred IO.

As will be more fully described, at the lower end of the said belt 2,charges of one sign are established on the said moving belt, and at itsupper end the charges carried thereby are removed and transferred to thehollow electrode or terminal 1. If the upper inductor is maintained at anegative potential with respect to the pulley which is connected to theterminal, then, simultaneously, charges of opposite sign are transferredfrom the electrode or terminal 1 to the belt 2 at its upper end and arecarried by the descending run to the lower end, where they are removed.

In Fig. 1 the pulley 3 is shown as connected to ground at 4a, and theinductor or inducting plate 5 is shown as connected at 4b to anelectromagnetic source of charge supply, conventionally indicated, butwhich may comprise a source of rectified alternating current utilizing atransformer and a vacuum tube rectifier.

In both Figs. 1 and 2 are represented at 40 columns of equipotentialplanes as a means for controlling the field due to the belt charge.These planes are separated one from the other by solid insulators, suchas glass or porcelain, and they are held at the proper potential byallowing a small current to flow along the columns through resistorsconnected between the planes. Each equipotential plane contains a seriesof conductors extending transversely across the entire width of each runof the belt 2 and on each side thereof, each separated from the belt 2by a relatively small distance.

In the embodiment of the apparatus of our invention shown in Figs. 1 and2, a negative electric charge is induced to flow on the ascending run ofthe belt 2, by maintaining a positive potential on a lower inducing orinductor plate 5 closely spaced with respect to the outer surface ofsaid belt 2, and shown as curved so as to be in substantial parallelismwith the belt 2 in the region where it is in contact with the lowerpulley and for some distance beyond on the departing side. At the upperpulley 4, shown in Fig. 2, we provide a similar inducing or inductorplate 6 also closely spaced with respect to the outer surface of thebelt 2, and similarly curved, so as to be in substantial parallelismwith the adjacent portion ofthe belt in the region of pulley contact andfor some distance beyond as shown. At said upper pulley 4, if theinductor plate 6 and the pulley 4 are at the same potential, then thecharge flows from the belt 2 to the pulley 4, when they becomeconductively connected.

The flow to the pulley 4 is due to the electric field of the chargewhich exists on the belt 2.

Fig. 2 shows the manner in which electric charge may be removed from theascending run of the belt 2 by means of a conductive contact (such asthe small pulley) within the electrode or terminal 1. The charge soremoved is conducted to the upper inducing or inductor plate 6 andthence to the high voltage electrode or terminal 1 through theresistance R. The IR drop in the resistance R supplies the electricfield between the upper inducing or inductor plate 6 and the upperpulley 4, which is directly connected to the terminal, to cause electriccharge of the opposite sign to flow conductively from the pulley 4 ontothe surface of the descending run of the belt 2.

In the inductive conductive charging system herein disclosed andclaimed, it is not necessary that the entire belt be of asemi-conducting character. We prefer to use a belt which is essentiallyinsulating except for a relatively thin semi-conducting sheath on itsinner surface. This appears to have the advantage that thesemi-conducting sheath can be made of relatively lower resistivitymaterial for a given leakage of electric charge along the belt under theimpetus of the voltage of the generator.

Such a semi-conducting sheath applied to the inner surface of the belt 2is indicated at 7 in both Figs. 1 and 2. It may extend over the entireinner surface of the said belt 2 and that is the construction indicatedin Figs. 1 and 2.

Alternatively, we have produced a suitable semi-conducting belt byintroducing the semi-conducting material on isolated areas of aninsulating belt structure. These isolated areas may be of differentform. In Fig. 3 they have the form of broken, spaced lines 8 extendingtransversely of the belt from substantially edge to edge. In- Fig. 5they have the form of circular areas 9, preferably symmetricallyarranged in parallel transverse rows, extending substantially from edgeto edge of the belt 2, and in Fig. 4 they take the form of a greatmultiplicity. of dots 10 extending preferably from edge to edge of thebelt 2.

Our invention, in accordance with which the charge conveyor, desirablyof an endless character, and is here shown as an endless belt 2, butwhich as stated in the preliminary description herein may be a large,rapidly rotating disk, has a semi-conductive inner surface. It isradically distinguished from an insulating belt carrying conductiveelements. The latter type of belt is not new in the art, it having beensuggested in the Van de Graafi Patent No. 1,991,236, but thererepudiated, as shown by the following quotation from lines to 62 of page4 of the specification of said patent as follows:

The use of conducting spots or zones on a belt or disk type of chargecarrier operating in air is, contrary to the prior practice, to beavoided as it results in decreased efficiency due to the lessenedeffective surface for transferring charges and may materially reduce themaximum voltage that may be established on the electrode or terminal.This will be apparent since a conducting spot or zone on the chargecarrier forms, at the instant that it enters the slot in the wall of theelectrode, a relatively sharp edged extension of the electrode, thuspromoting a corona or leakage discharge from the electrode.

A conductor-carrying belt has the limitation that the conductiveelements are usually metals of exceedingly high conductivity and must bespaced relative to one another along the surface of the insulating andsupporting belt structure in order that the charge may remain isolatedon the conductive elements and that a high voltage may be insulatedalong the belt length. While such conductorcarrying belts may be builtboth in principle and in fact, they would possess inherent disadvantagesbecause of the physical inhomogeneity of the composite belt, the naturalreduction in its voltage insulating ability, the presence of sharp edgeson the conductive elements and the impossibility of utilizing the entirebelt surface for charge carrying purposes.

-In contrast to this, a belt constructed in accordance with ourinvention of the proper semi-conducting material may use its entiresurface for the deposition and transfer of electric charge. It hasstructural homogeneity; it is comparatively free from the high electricfields associated with metallic conductive elements, and it isinherently capable of insulating higher voltages in the same overalllength. The use of semi-conducting material in this manner is new in theart and. special techniques must be used to obtain such conductivity asto permit the conductive transfer of charge to' the belt under theaction of an inducingfield and yet allow this charge to remain fixed tothe belt surface during its passage toward the electrode system on whichthis charge will be stored.

We have found that the resistivity of this semi-conducting material mustlie in the range from ohm cm. to 10 ohm cm., depending upon such factorsas the desired charge density, the available voltage gradient, the speedof; the belt and pulley size, and the intimacy of contact betweenbeltand charge source. This range of resistivity is in marked contrast tothat which is conventionally used in' the ionization methods of chargetransfer. Therein the belt resistivity is commonly of the order of 10 to10 ohmcm. and rarely less than 10 Our semi-conductin g'belts' may beused with conventional charging systems The semi conducting belts hereindisclosed can be used in Van de Graaff voltage sources which utilize theionization method of charge deposition and removal from the beltsurface. By directing a row of points toward a metal pulley and applyingan appropriate potential between them, electric charges of the polaritycharacteristic of the pointed system will be directed toward theintervening belt and deposited upon it. This is true whether the belt beof the conventional insulating nature or one which possesses asemi-conducting surface of the general characteristics that we haveherein described. The semiconducting belt may possess an advantage inthat the charge would tend to distribute itself more uniformly over theavailable belt surface and since unwanted surface charges produced byfriction would be minimized.

Effects of induction conduction charging The novel, herein disclosedmethod of electrically charging the charge conveying belt system of theVan de Graalf accelerators has the following effects:

1. It eliminates ionization of the gaseous medium with its resultingenergy loss, dissociation of the gas molecules, deterioration of thebelt material and corrosion of metal surfaces.

2. It is free of the polarity effects of the ionization method whichgenerally made it more difficult to deposit positive charge upon beltsurfaces at the higher gas pressures.

3; It permits unrestricted use of superior gaseous dielectrics as theessential insulating medium for Van de Graaff accelerators. Suchsuperior dielectrics include the electronegative gases such as Freon(CCl2F2) and sulfurhexafiuoride (SP6).

4. It is largely free of the unsteadiness of charge transfer which wasdue to difficulties in maintenance of sharp points and screen edges andtheir spacing relative to the belt and pulley.

5. The charge transferred by our herein disclosed, novel method isindependent of the nature of the gas and is directly proportional to theinducing potential Y.

6. Higher charge densities can be carried by the semiconducting beltsystem because the electric charge can be more uniformly distributedover the belt surface.

7. The voltage insulating strength of the belt may be increased becausethe charge is more uniformly applied and the belt is free of thecondition of ionization at its grounded and high potential ends.

Without limiting ourselves thereto, as the materials any one of which wecan apply to the inner surface of the belt 2 orother semi-conductingcharge conveyor as the layer or coating 7, 8, 9 or 10, we state that asemi-conducting material suitable for the purposes of this invention canbe made of a rubber compound using neoprene rubber and tricr'esylphosphate as a plasticizer which further increases the conductivity ofneoprene. A temporarily satisfactory method of rendering the innersurface of the insulating belt or charge carrier of the proper degree ofsemi-conductivity is by coating it with Carbowax, which is polyethyleneglycol. Other forms of rubber may be used, such as Hycar, which alreadypossesses a considerable conductivity in comparison with natural rubber,but requires the further inclusion of some material" to bringresistivity down to the range of 10 ohm cm. to 10 o hm'cm. In principleit would be possible to add carboncontaining materials to rubber inorder to secure the desired degree of conductivity.

The semi-conducting material may be distributed uniformly over the innerbelt surface, or as shown in Figs. 3, 4 or 5. Then again, thesemi-conducting surface may be made of a material which extends wellinto the volume of the belt. Within the invention the semi-conductingcoating may be characteristic of the semi-conducting nature of theentire belt structure. In any case, the semiconducting belt 2 permitsthe flow of electric charge to and from the belt 2 surface, but resiststo an almost complete extent the flow of electric charge lengthwise thesaid belt 2.

The lower and upper inducting or inductor plates 5, 6, are preferablymade of metal such as aluminum, steelor brass.

It will be evident from the foregoing description that in accordancewith our invention, electric charge is deposited upon the belt or othermoving charge conveyor by providing a semi-conducting layer on the innersurface of the belt or other conveyor, and electrostatically inducingcharge to flow between the conductive surface of a pulley or the likeand the semi-conductive surface of the belt or other moving chargeconveyor, during the interval they are in contact. The charge flows tothe belt or other moving charge conveyor from the conducting pulley (inthe case of a belt) or from its substitute or equivalent, if some otherform of charge conveyor is employed. The charge is similarly conveyedfrom the belt.

Each of the inductor or inducting plates 5 and 6 is closely spaced withrespect to the belt 2 and produces an electric field between such beltand the respective conductive pulleys 3 and 4. g p

The belt 2, constructed as herein described, is capable of insulatinghigh electric gradients along its length, and it has a semi-conductingsurface layer, desirably of resistivity 10 to 10 ohm cm. In oneembodiment such inner surface layer may be composed of such materialthat its resistivity is lowered to a value in the range below 10 ohm cm.by an increase in its temperature, during the interval it is in contactwith a heated pulley such as 3 and 4', and its resistivity increasesduring the interval it is' not in contact with the pulleys.

It will be evident from the foregoing description that we have providedhigh voltage apparatus and system consisting of a metallic terminalinsulated and supported from ground, a rapidly moving belt passingbetween ground and a region with such terminal, an inductor plateclosely spaced to the said belt and producing an electric field betweenthe said belt and the metal, conductive pulley at the grounded end ofthe system, the said belt being coated preferably in the manner and tothe extent described with a materialof such semi-conducting nature thatelectric charge can flow from said pulley to said belt, and can alsoflow from said belt to a conductive pulley within the terminal, therebeing an inductor or inducing plate closely spaced with respect to saidconductive pulley within the terminal.

It is further to be understood that the semi-conducting layer is of suchinnate conductivity as to permit the acquisition during the interval ofcontact with the respective pulleys, of a surface charge densityapproaching the maximum that can be insulated in the gaseous mediumwithin the tank that surrounds the described parts, such as thatillustrated at 21 in Fig. l of the U. S. patent to Trump No. 2,252,668,or illustrated at 4 inFig. l of the patent to Trump and Cloud No.2,503,224.

Our invention includes, and we hereby specifically make disclosure of aplurality of insulating belts passing at high linear velocity betweenground and an electrode terminal, each of said belts being coated ontheir surfaces, and specifically upon their inner surfaces with asemi-conducting material.

Having thus disclosed one embodiment of the apparatus of our invention,and by means of which the system and method of our invention may bepracticed, we desire it to be understood that although specific termsare employed, they are used in a generic and descriptive sense, and notfor purposes of limitation, the scope of the invention being set forthin the following claims.

We claim:

1. Induction-conduction charging means in a high potential electrostaticapparatus including a chamber or tank containing gas under high pressurecomprising a metallic or other conductive surface, and a moving chargeconveyor having at least one semi-conductive surface, and meanselectrostatically to induce electric charge to a surface and such movingcharge conveyor.

flow Without gaseous ionization between such conductive 2.Induction-conduction charging means in a high potential electrostaticapparatus including a chamber or tank containing gas under high pressurecomprising a rapidly moving charge-carrying belt having asemi-conductive inner surface, a metallic or other conductive surface incontact with said belt, and means electrostatically to induce electriccharge to flow without gaseous ionizaation between such conductivesurface and the semi-conductive surface of such charge-carrying beltduring the interval of contact.

3gInduction-conduction charging means in a high potential electrostaticapparatus including a chamber or tank containing gas under highpressure, comprising a metallic terminal insulated and supported fromground, a moving, charge-conveyor belt having as an essential element asemi-conducting surface and passing from a region at ground potential toa region within such metallic terminal, and electrostatic inductionmeans for transferring charge from ground to said belt and from saidbelt to said terminal without gaseous ionization, there being aconducting pulley with which said chargeconveyor belt is in contact,said belt being provided upon its surface with a semi-conducting layerto or from which charge flows during the interval such belt and pulleyare in contact.

4. That-system of transferring electric charge in a high potentialelectrostatic apparatus and thereby eliminating the necessity of gaseousionization in transferring electric charge to and from the moving chargeconveyor thereof wherein there is provided an endless traveling conveyorhaving a semi-conducting surface, and wherein there is provided ametallic or other conductive surface, and wherein means is provided forelectrostatically inducing electric charge to flow without gaseousionization between such metallic or other conductive surface and thesemi-conducting surface of said endless traveling conveyor.

' 5. Induction-conduction charging in a high potential electrostaticapparatus and thereby eliminating the necessity of gaseous ionization intransferringelectric charge to and from themoving charge conveyorthereof, comprising a rapidly moving charge-carrying belt havingsemi-conducting ,material distributed in lines extending transverse tothe direction of motion of such belt, upon the inner surface thereof, aconductive pulley about which said belt passes, and meanselectrostatically to induce electric charge to flow betweensuch'pulleyand such inner surface of said belt.

6. Induction-conduction charging in a high potential electrostaticapparatus, and thereby eliminating the necessity of gaseousionization intransferring electric charge to and from the moving charge conveyorthereof, comprising a rapidly moving charge-carrying belt havingsemi-conducting material distributed in the form of small spaced areason the inner surface of such belt, a conductive pulley about which saidbelt passes, and means electrostatically to induce electric charge toflow between such pulley and such inner surface of said belt.

7. High-voltage charging in a high potential electrostatic apparatus,and thereby eliminating the necessity of gaseous ionization intransferring electric charge to and from the moving charge conveyorthereof, consisting of a well-insulated metal terminal from ground, arapidlymoving belt, a conductive pulley in the region of groundpotential, and a conductive pulley within said terminal and about bothof which said belt passes, inductor plates closely spaced to said beltand in the operation of the apparatus producing electric fields betweensaid belt and the said pulleys, the said belt having a coating of amaterial of such a semi-conducting nature that electric charge can flowbetween said pulleys and said belt.

8. High-voltage apparatus consisting of a metallic terminal insulatedand supported from ground, a rapidly moving belt passing between groundand a region within said terminal, said belt having an inner surfacelayer of such material that its resistivity is lowered to a value in therange below 10 ohm cm. during the interval that it is in contact with aheated pulley about which it passes and a chamber or tank to contain gasunder pressure and within which the said apparatus is located.

9. High voltage apparatus consisting of a well-round ed metallicterminal insulated in a gaseous medium from ground, acolumn ofalternatelyarranged insulating and.

conducting members for the physical support of said terminal,'ametallicor other conductive pulley within said terminal, a metallic or otherconductive pulley in a region near ground potential, an endless'belt ofinsulating material passing over said pulleys, the said belt beingcoated on its inner surface with a layer of semi-conductive material,two inductor plates, respectively closely spaced to said belt at each ofsaid pulleys, means to establish an electric field between said inductorplates respectively and said pulleys so as to cause the flow of electriccharge between said pulleys and the semi-conducting layercoating on saidbelt, the said semi-conducting layer being of such innate conductivityas to permit the acquisition during the interval of contact with saidpulleys, of a surface charge density approaching the maximum that can beinsulated in said gaseous medium.

l0. High-voltage apparatus consisting of a well-rounded metallicterminal insulated in a gaseous medium from ground, a column ofalternately arranged insulating and conducting members for the physicalsupport of said terminal, a metallic or other conductive pulley withinsaid terminal, a metallic or other conductive pulley in a region nearground potential, an endless belt of insulating material passing oversaid pulleys, the said belt being coated on its inner surface with alayer of semiconductive material, two inductor plates respectivelyclosely spaced to each belt at each of said pulleys, means to establishan electric field between said inductor plates respectively and saidpulleys, so as to cause the flow of electric charge between said pulleysand the semi-conducting layer coating on said belt, the said layer ofsemiconductive material having a resistivity of 10 to 10 ohm cm.

11. High voltage apparatus consisting of a metallic terminal insulatedin a gaseous medium from ground, insulating means for the physicalsupport of said ter minal, a conductive pulley within said terminal, aconductive pulley-in a, region near ground potential, an endless belt ofinsulating material passing over said pulleys, two inductor plates,respectively closely spaced to said belt at each of said pulleys, andmeans to establish an electric field between said inductor platesrespectively and said pulleys so as to cause the flow of electric chargebetween said pulleys and the said belt, thereby eliminating thenecessity of gaseous ionization.

12. High voltage apparatus consisting of a metallic terminal to whichcharges are transferred, insulating means for the physical support ofsaid terminal, an endless traveling belt constituting a charge conveyor,means for electrostatically inducing charge to flow onto said belt, ametal charging pulley with which successive portions of said belt aremomentarily in contact, and means for inducing the charges to flow fromthe said belt to said metallic terminal, the means for electrostaticallyinducing charge to flow onto said belt including an inductor plateclosely spaced with respect to the outer surface of said belt, and themeans for electrostatically inducing charge to flow from said belt tosaid terminal including an inductor plate closely spaced with respect tothe outer surface of said belt and in proximity to said terminal,thereby eliminating the necessity of gaseous ionization.

13. High voltage apparatus consisting of a metallic terminal to whichcharges are transferred, insulating means for the physical support ofsaid terminal, an endless traveling belt constituting a charge conveyor,means for electrostatically inducing charge to flow onto said belt, ametal charging pulley with which successive portions of said belt aremomentarily in contact, and means for inducing the charges to flow fromthe said belt to said metallic terminal, the means for electrostaticallyinducing charge to flow onto said belt including an inductor plateclosely spaced with respect to the outer surface of said belt, and themeans for electrostatically inducing charge to flow from said belt tosaid terminal including an inductor plate closely spaced with respect tothe outer surface of said belt and in proximity to said terminal, saidendless traveling belt being essentially insulating but with arelatively thin semi-conducting sheath at its inner surface, therebyeliminating the necessity of gaseous ionizatron.

14. High voltage apparatus for electrostatically inducing a flow ofcharge to a charge conveyorwithin a chamber containing gas under highpressure, and without re sulting gaseous ionization, comprising thefollowing: a chamber provided for the purposeof and adapted to contain agaseous medium under high pressure; a charge conveyor of asemi-conducting character within said chamber; means to impart rapidtraveling movement to said charge conveyor within said chamber when sofilled with gas under high pressure; an inductor member within thechamber and closely spaced to the conveyor; and a source of chargesupply for maintaining a potential of one sign upon said inductormember; said semi-conductive conveyor and said maintained-potentialinductor member constituting means for electrically inducing electriccharge of opposite sign to flow from said inductor member to said chargeconveyor while the latter is so traveling Within said chamber, andwithout creating gaseous ionization within said chamber with resultingdissociation of gas molecules that would increase their chemicalactivity.

15. High potential electrostatic apparatus wherein, for transferringelectric charge to and from a metallic terminal, there is provided anendless belt that passes over pulleys having conducting surfaces, andwhich belt is essentially of an insulating character of material, butwhich belt is provided upon its inner surface that contacts with saidpulleys with a relatively thin semi-conducting sheath of relativelylower resistivity material for a given leakage of electric charge alongthe belt under the impetus of the voltage of the generator, theresistivity of such semi-conducting sheath lying in the range from 10ohm cm. to 10 ohm cm.

16. High potential electrostatic apparatus in accordance with claim 15,wherein the semi-conducting sheath is a rubber compound.

17. In the generation of high potential electrostatic charges in agas-pressurized chamber, the step which comprises rapidly moving asemi-conducting charge conveyor surface in the chamber in passingcontact with a metallic or other conductive surface and in closelyspaced proximity to an inductor thereby to transfer electric charge fromone to the other surface with avoidance of attendant gaseous ionization.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 479,941 Henry Aug. 2, 1892 2,070,972 Lindenblad Feb. 16, 19372,486,140 Felici Oct. 25, 1949 2,568,824 Rahbek Sept. 25, 1951

